Combinatorial chemistry refers to techniques to fabricate, test, and store the resulting data of a material library containing tens, hundreds or even thousands of different materials or compounds. Combinatorial investigations require rapid screening techniques to test and evaluate variations of composition, structure and property within a material library. X-ray diffraction analysis is one of the most suitable screening techniques of solid state properties because abundant information can be revealed from the diffraction pattern, and X-ray diffraction analysis is fast and non-destructive.
Diffraction pattern analysis plays an important role in such diverse applications as solving molecular structures, identifying compounds, and fabricating materials. If a compound can be crystallized into sizeable crystals, diffraction patterns from single crystals can provide information about the crystal structure of the compound. Many compounds, however, can only be obtained as powders. Although a powder diffraction pattern yields much less information than that generated by a single crystal, it is unique to each substance with a particular crystal structure, and is therefore highly useful for purposes of identification.
Scattering of incident X-ray radiation from a sample of material can yield information about the atomic structure of the material. When such a beam of radiation strikes a sample, a pattern of diffracted radiation is created, which has a spatial intensity distribution that depends on the wavelength of the incident radiation and the atomic structure of the material. The spatial intensity distribution can be recorded on a suitable detector such as a point detector, a 1D detector or a 2D detector. Diffraction analysis is a method of studying crystalline materials, crystallization behavior, and liquid, gel or solid phase, or phase transitions of materials.
In certain circumstances, it is desirable to perform a sample analysis using transmission mode X-ray diffraction analysis for various reasons, including the need for low angle diffraction, and advantages when testing thin samples or samples in liquid environments.
A problem that is encountered with known powder diffraction analysis equipment using a 2D detector is that during detection of the diffraction radiation, single diffraction spots and arcs are often observed instead of rings, especially when organic crystalline material (such as pharmaceuticals) is irradiated. This may result from the fact that not all lattice planes of the crystalline powder material have or have not been exposed to X-ray radiation for the same time or the same amount, because the crystals were not random oriented or only a few crystals were present. As a result, the peak intensities of the powder diffraction patterns recorded with a point or a 1D detector (one-dimensional detector) are not correct, and no representative 1D-powder diffraction pattern (intensity vs. diffraction angle 2θ.) is created. This causes problems during comparison of diffraction patterns for identification.